Production of haloprenes



the 1,2-dihalo-3-butenes.

Patented Nov. 4, 1947 PRODUCTION OF HALQPRENES George W. Hearne,

El Cerrito, and Donald S. La France, Richmond, CaliL,

assignors to Shell Development Company, San Francisco, Calif., acorporation of Delaware No Drawing. Application September 5, 1946,Serial No. 695,052

16 Claims. (01. 260-655) 1 This invention relates to a practical andeconomical method for producing 2-halo-1,3-butadienes, referred tohereinafter as the haloprenes by analogy with chloroprene(2-chlorobutadiene- 1,3) which is the most important, commercially,

of this class of compounds due to the fact that chloroprene is theessential component of neoprene rubber.

In the past acetylene has been the only source of commercial chloropreneand a complicated procedure, involving the intermediate production ofvinyl acetylene, has been necessary in chloroprene manufacture. This hasmade chloroprene a relatively expensive compound and has materiallyrestricted the use of neoprene in spite of its many special advantagesover other types of synthetic rubber. The present invention is ofparticular value in that it provides a simple and efficient processwhich is especially well adapted to the large scale production ofchloroprene from a cheap starting material, namely,1,2-dichlorobutene-3, which may be readily obtained by chlorinatingbutadiene.

The invention is not limited to the production of chloroprene, however,and an important object is the'provision of a relatively simple anddirect method for the production of haloprenes from Another object is toprovide an economically practical method of converting1,2-dihalo-3-butenes to haloprenes which can readily be carried outcontinuously on a largescale. A special object isto produce haloprenes,particularly chloroprene, in high yields from 1,2- dihalo-3-butenes.Further objects and advantages of the invention will be apparent fromthe following description of the new process.

According to the invention, haloprenes are produced by .treating a1,2-dihalobutene-3 with an aqueous solution of an alkali at atemperature at least equal to the boiling temperature of the halopreneunder the reaction conditions and separating the haloprene produced fromthe reaction mixture. This method of operation has several importantadvantages over other methods for converting a 1,2-dihalobutene-3 to ahaloprene. In this connection it must be noted that, although hightemperature pyrolysis of other dichlorbutenes such as2,3-dichlorbutene-l, does produce chloroprene the pyrolysis of either1,2-dichlorbutene-3 or 1,4-dichlorbutene-2 forms l-chlorbutadiene-l,3instead of 2-chlorbutadiene-l,3 (chloroprene). In order to producechloroprene, it has been proposed to treat 1,2-dichlorbutene-3 withsolid caustic alkali. This is described in Carothers patentU. S.2,038,538. In accordance with one of the embodiments of the presentinvention it has been found that yields greatly exceeding thoseobtainable by the previously proposed method may be attained byemploying an aqueous solution of an alkali, such as sodium hydroxide,potassium hydroxide, calcium hydroxide, sodium carbonate, etc. Accordingto this process, the 1,2-dichlorbutene-3 to be dehydrochlorinated isintroduced into a. solution of the alkali, such as a 10% aqueous sodiumhydroxide solution, preferably with stirring or agitation.-

The solution is maintained above the boiling point of chloroprene (i.e., about 60- C.) and preferably at the boiling point of the alkalisolution. The reaction producedchloroprene which vaporizes due to theelevated temperature employed.

In order to avoid undesirable side reactions, the chloroprene should beremoved substantially as rapidly as formed. The dehydrochlorination canalso be effected with aqueous sodium carbonate or calcium hydroxide atabout their boiling points. what slower than when efiected with aqueoussodium hydroxide. Also, possibly due to the longer contact period at therelatively high temperatures, some of the chloroprene was found to bepolymerized during the treatment with aqueous solutions of alkaliesother than the alkali metal hydroxides.

It has been proposed in Lange patent-U. S. 2,180,115 to use anhydroussolutions of alkalies, particularly alcoholic alkali, for the productionof chloroprene from 1,2-dichlorbutene-3, but this method also is lessadvantageous than the process of the present invention. By the use ofaqueous solutions of alkali, not only may increased yield of the desiredhaloprenes be obtained, but also the economy and ease of operation areimproved, particularly with respect to the recovery of the productswhich are substantially insoluble in water and boil at temperaturessufliciently different from that of water so that they are easilyseparated without resort to the elaborate procedures which are necessarywhen organic solvents are used.

As previously indicated, the preferred aqueous alkali solutions for usein the process are solutions of alkali metal hydroxides, sodium. andpotassium hydroxides being particularly suitable because of their lowcost. However, equally satisfactory results can be obtained withaqueous-ammonium, lithium or rubidium hydroxides lnstead of the alkalimetal hydroxides,tl 1e corresponding carbonates such, for example, as

s dium carbonate, potassiumcarbonat'e, nd the' The reactions are,however, some-' DIOCESS.

like may be used. Aqueous solutions of the alkaline earth metalhydroxides such as magnesium, calcium, strontium and barium hydroxidesmay also be used with good results for the dehydrohalogenation of1,2-dihalo-3-butenes according to the invention. Regardless of theparticular aqueous alkali chosen, it is advantageous to maintain theconcentration of alkali in the solution between about 1% and about 30%,preferably between about and about 15%, by weight. The desiredconcentration may be conveniently maintained by continuously orintermittently adding make-up alkali to the solution. The addition maybe made directly to the reactor or a part of the solution may beWithdrawn and alkali added before recycling the solution to the reactor.In either case it may be desirable to continuously or intermittentlydiscard a part of the solution or remove therefrom the chlorides formedin the reaction in order to prevent an excessive accumulation of suchmaterials in the system.

As a rule, it is desirable to employ such a volume of aqueous alkali inthe reaction as will insure the presence of a substantial stoichiometricexcess'of alkali based on the 1,2-dihalobutene-3 to bedehydrohalogenated. Very large excesses may be used, the only limitbeing those imposed by the volume of solution involved which, of course,should not be so great as to unduly burden the reaction system.

With any of the previously described aqueous alkali solutions, thereaction may be carried out at a temperature at least equal to theboiling temperature of the haloprene or haloprenes being produced. Anupper temperature limit is the boiling temperature of the aqueous alkalisolution used. For ease of control, the dehydrohalogenation ispreferably carried out at the boiling temperature of the aqueous alkaliunder the reaction conditions because this temperature can readily bemaintained with minimum attention from the operator. However, lowertemperatureswhich are sufficient to vaporize the haloprene have beenfound to be effective in the When Operating as preferred at the normalboiling point of the aqueous alkali solution, it is desirable tocondense the. distillate from the reaction and return the aqueous layerof the condensate to the reaction, preferably as reflux.

The process is particularly adapted for continuous operation, but mayalso be carried out 'batchwise or intermittently; Normal pressures maybe maintained advantageously but higher or lower pressures are alsosuitable. Still other variations in the process may be made withoutdeparting from the invention.

The following example is presented to illustrate a preferred method forthe production of g. high'yields of chloroprene from butadiene using theprocess of the invention:

. Example I Butadiene-1,3 and chlorine were separately preheated to atemperature of about 150 C., and were then intimatelycommingled in amolal ratio of about 4 to 1. The mixture was then conveyed through areaction chamber filled with carbon chips and maintained at atemperature of between about 150 C. and 190 0., the rate of passage ofthe gaseous mixture being such that 1.26 gm. of chlorine were introducedinto the chamber per minute. The reaction products showed that yield of1,2-dichlorbutene-3 and ,4- dichlorobutene-2 was about 70 mol per centbased l,2,3,4-Tetrachlorbutane on the chlorine applied, the exactcomposition of the product being:

Yield in mol per cent of Reaction product chlorine appliedMonochlor-diolefin 1,2-Dichlorbutene-3. 1,4-Dichlorbutene-2.

Polymer The 1,2-dichloride obtained directly by the chlowatercontinuously by fractionation.

rination of the butadiene and that obtained by the catalytic allylicrearrangement were then slowly added to a boiling 10% sodium hydroxidesolution. The mixture was maintained in a state of agitation, and thechloroprene formed as the result of this reaction was distilled offsubstantially as rapidly as it was formed. It was found that about 94%of the dichloride was converted to chloroprene, or approximately a yieldof 65.8% based on the butadiene treated.

Although only a 65.8% yield was recovered, this yield is far greaterthan that heretofore obtainable by operating according to the knownprocesses. Also, the above yield could be further increased by employingefficient recovery systems. This is due to 'the fact that it was noticedthat relatively large handling losses were produced in theabove-described process, particularly in the recovery of the unsaturateddihalides produced during the vapor phase halogenation of the diene.This loss, if recovered by properly designed means, would furtherincrease the actual yield of the final product.

The following example shows the advantage, particularly with respect toyield of chloroprene, obtainable by the process of the inventioncompared with methods using solid alkalies or alcoholic alkalisolutions.

Example II 1,2-dichlobutene-3 was fed at a, liquid hourly space velocityof 0.165 into a boiling 10% aqueous. sodium hydroxide solution. Themixture was maintained in a state of agitation and the chloropreneformed was removed as an azeotrope with It was found that the conversionto chloroprene was equal to about 86%, based on the 1,2-dichlorbutene-3introduced, and that the yield of chloroprene was equal to about 96% ascalculated on the dichlorbutene consumed.

When 1,2-dichlorbutene-3 was treated with solid sodium hydroxide in theproportions of 210 grams of sodium hydroxide to 106 grams of thedichlorbutene, using a temperature of about C., and distilling off andanalyzing the overhead vapors from the reaction, it was found that theyield of chloroprene was equal to only about 65% based on the1,2-dichlorbutene-3 consumed.

In another run 1,2-dichlorbutene-3 was mixed with a Z-normal alcoholicpotassium hydroxide solution, and the mixture was then subjected toa'distillation under a subatmospheric pressure. An analysis of thereaction products showed that chloroprene was thus produced in a yieldof 67%,

based on the amount of the dichlorbutene introduced into the reactionzone.

Other haloprenes may be produced in the same way as shown by thefollowing examples:

Example III Example IV 1,2-dichlorbutene-3 was slowly added to arefluxing saturated lime'solution and the chlordprene distilled off asfast as formed. The conversion based on the 1,2-dichlorbutene-3 consumedwas about '71 Example V Using a sodium carbonate solution ofconcentration in place of the lime solution of Example IV, a fairconversion to chloroprene, based on the 1,2-dichlorbutene-3 consumed,was obtained.

It will be seen that the process of the invention is capable of widevariation, not only with respect to 'the 1,2-dihalo-3-butenes whichm'aybe .reacted and the aqueou alkali solutions which may be used, but alsoin regard to the method of operation and the conditions under which thereaction may be carried out. Thus, for example, it is oftenadvantageous, particularly when using aqueous alkalies in the form ofthe carbonates or alkaline earth metal hydroxides, to carry out thereaction in the presence of a polymerization inhibitor such, forinstance, as catechol, p-tertiary butyl phenol, hydroquinone, or thelike. Also, in the production of iodoprene from a 1-halo-2-iod0-butene-3, a reduced pressure of the order of about 500 mm. Hg or less isadvantageous. Still other variations may be made in the invention whichis not limited to the details disclosed by way of example nor by anytheory proposed in explanathan the boiling temperature of chloroprene,and

distilling chloroprene from the reaction mixture substantiallyas soon asit is formed therein.

4. A process for the conversion of 1,2-dichlorbutene-3 to chloroprenewhich comprises treating the 1,2-dichlorbutene-3 with an aqueous sodiumhydroxide solution at about the boiling temperature of the sodiumhydroxide solution, and distilling chloroprene from the reaction mixturesubstantially as soon as it is formed therein.

5. A process for the conversion of 1,2-dichlor- I butene-3 tochloroprene which comprises treating tion of the improved results whichare achieved.

This application is a continuation-in-part of copending applicationSerial No. 429,390, filed February 3, 1942, and of copending applicationSerial No. 303,098, filed November 6, 1937, of which said applicationSerial No. 429,390'is a division.

We claim as our invention:

1. A process for the conversion of 1,2-dichlorbutene-3 to chloroprenewhich comprises; introducing 1,2-dichlorbutene-3, at about the rate atwhich it is consumed by the reaction, into 'an aqueous sodium hydroxidesolution which is agitated and maintained at about its boiling temper,-ature, and distilling chloroprene from the reaction mixturesubstantially as soon as it is formed therein.

2. A process for the conversion of 1,2-dichlorbutene-3 to chloroprenewhich comprises introducing 1,2-dichlorbutene-3 into an aqueous sodiumhydroxide solution maintained at a tem-- perature greater than theboiling temperature of chloroprene, and distilling chloroprene from thethe 1,2-dichlorbutene-3 with an aqueous sodium hydroxide solution at atemperature greater than the boiling temperature of chloroprene, anddistilling chloroprene from the reaction mixture substantially as soonas it is formed therein.

6. A process for the conversion'of 1,2-dichlorbutene-3 to chloroprenewhich comprises treating the 1,2-dichlorbutene-3 with an aqueous sodiumhydroxide solution at a temperature greater than the boiling temperatureof chloroprene, and separating chloroprene from the reaction mixture.

7. A process for the conversion of 1,2-dichlorbutene-3 to chloroprenewhich comprises treating the 1,2-dichlorbutene-3 with an aqueous sodiumhydroxide solution at a temperature at least equal to the boilingtemperature of chloroprene, and separating chloroprene from the reactionmixture.

8. A process for the conversion of 1,2-dichlorbutene-3 to chloroprenewhich comprises treating the 1,2-dichlorbutene-3 with an aqueoussolution of an alkali at a temperature at least equal to the boilingtemperature of chloroprene, and separating chloroprene from the reactionmixture.

9. A process for the conversion of 1,2-dichlorbutene-3 to chloroprenewhich comprises treating the 1,2-dichlorbutene-3 with an aqueouspotassium hydroxide solution at about the boiling temperature of thepotassium hydroxide solution, and distilling chloroprene from thereaction mixture substantially as soon as it is formed therein.

10. A process for the conversion of 1,2-dichlorbutene-3 to chloroprenewhich comprises treating the 1,2-dichlorbutene-3 with an aqueous alkalimetal hydroxide solution at about the boiling temperature of saidaqueous solution, and distilling chloroprene from the reaction mixturesubstantially as soon as it is formed therein.

11. A process for the conversion of 1,2-dichlorbutane-3 to chloroprenewhich comprises treating reaction, into an aqueous sodium hydroxidesolution which is agitated and maintained at about its boilingtemperature, and distilling the Z-halobutadiene-1,3 produced fromthe-reaction mixture substantially as soon as it is formed.

13. A process for the conversion of a 1,2-dihalobutene-3 to a2-halobutadiene-1,3 which comprises treating the 1,2-dihalobutene-3 withan aqueous solution 01' an alkali metal hydroxide at about the boilingtemperature of said aqueous solution and distilling the2-ha1obutadiene-'1,3 produced from the reaction mixture substantially assoon as it is formed.

14. A process for the conversion of a, 1,214.11-

halobutene-i; to a 2-ha1obutadiene-1,3 which comprises treating the1,2-dihalobutene-3 with an aqueous solution of an alkali at atemperature at least equal to the boiling temperature of the2-halobutadiene-1,3 which is produced and separating said2-halobutadiene-L3 from the reaction mixture.

15. A process for the conversion of a 1,2-dihalobutene-3 to a2-halobutadiene-1,3 which comprises treating a 1,2-dihalobutene-3 havinga chlorine atom linked to the terminal carbon atom with an aqueoussolution of an-alkali metal hydroxide at about the boiling temperatureof said aqueous solution and distilling the 2-halobutadime-1,3 producedfrom the reaction mixture substantially as soon as it is formed.

16. A process for the conversion of a 1,2-diprises treating a1,2-dihalobutene-3 having a bromine atom linked to the terminal carbonatom with an aqueous solution of an alkali at a temperature at leastequal to the boiling temperature of the 2-halobutadiene-1,3 which isproduced and separating said 2-halobutadiene-1,3 from the reactionmixture.

' GEORGE W. HEARNE.

DONALD S. LA FRANCE.

I REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,038,538 Carothers Apr. 28, 19362,180,115 Lange et al Nov. 14, 1939

